1. Field of the Invention
This invention is related to the field of graphical information processing, more particularly, to blending multiple layers of pixels.
2. Description of the Related Art
Part of the operation of many computer systems, including portable digital devices such as mobile phones, notebook computers and the like is the use of some type of display device, such as a liquid crystal display (LCD), to display images, video information/streams, and data. Accordingly, these systems typically incorporate functionality for generating images and data, including video information, which are subsequently output to the display device. Such devices typically include video graphics circuitry to process images and video information for subsequent display.
In digital imaging, the smallest item of information in an image is called a “picture element”, more generally referred to as a “pixel”. For convenience, pixels are generally arranged in a regular two-dimensional grid. By using this arrangement, many common operations can be implemented by uniformly applying the same operation to each pixel independently. Since each pixel is an elemental part of a digital image, a greater number of pixels can provide a more accurate representation of the digital image. The intensity of each pixel can vary, and in color systems each pixel has typically three or four components such as red, green, blue, and black.
Most images and video information displayed on display devices such as LCD screens are interpreted as a succession of image frames, or frames for short. While generally a frame is one of the many still images that make up a complete moving picture or video stream, a frame can also be interpreted more broadly as simply a still image displayed on a digital (discrete, or progressive scan) display. A frame typically consists of a specified number of pixels according to the resolution of the image/video frame. Information associated with a frame typically consists of color values for every pixel to be displayed on the screen. Color values are commonly stored in 1-bit monochrome, 4-bit palletized, 8-bit palletized, 16-bit high color and 24-bit true color formats. An additional alpha channel is oftentimes used to retain information about pixel transparency. The color values can represent information corresponding to any one of a number of color spaces.
In addition to the color values, the pixels may also have associated per-pixel Alpha values providing opacity information for the pixel. Alpha values may be stored what is commonly referred to as an Alpha channel, and each Alpha value may be between 0 and 1, with a value of 0 meaning that the pixel does not have any coverage information and is transparent, and a value of 1 meaning that the pixel is opaque. Based on this opacity information, various layers of an image frame may be blended together. In general, blending is the process of combining multiple layers of an image to overlay portion of one layer atop another layer, or to create the appearance of partial transparency of certain elements in some of the layers. For example, blending is used extensively when combining computer rendered image elements with live footage. In many cases blending operations include multiple layers that perform blending, where each level performs a normalization division. Over multiple levels of blending, the errors introduced by the normalization at each level may be compounded, resulting in less than the desired accuracy in how the blended images are displayed.
Other corresponding issues related to the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.